A fluorescence spectrophotometer is an apparatus for analyzing a sample by casting an excitation light onto the sample to bring it into an excited state and for measuring the intensity of fluorescence which is emitted when the sample returns from the excited state to the ground state.
A common type of fluorescence spectrophotometer is hereinafter described by means of FIG. 1 (Patent Document 1). The fluorescence spectrophotometer has a light source 1, an excitation-side light-dispersing device 2, a sample cell 3, an emission-side light-dispersing device 4 and a detector 5. The light produced by the light source 1 is dispersed by the excitation-side light-dispersing device 2 into a spectrum of light, from which only a monochromatic light having a desired wavelength λEx is cast into the sample cell 3. By this light of wavelength λEx, the sample contained in the sample cell 3 becomes excited and emits fluorescence. The emission-side light-dispersing device 4 and the detector 5 are provided for detecting the fluorescence emitted from the sample. The wavelength selected by the emission-side light-dispersing device 4 is adjusted at the fluorescence wavelength λEm. Since the fluorescence emitted from the sample is fainter than the light transmitted through the sample cell 3, the emission-side light-dispersing device 4 is located off the path of the irradiation light so that the transmitted light will not fall onto it. The detection result obtained with the detector 5 is fed to an output unit 6 and processed into a graph or the like.
Each of the excitation-side and emission-side light-dispersing devices 2 and 4 has a diffraction grating 21 or 41 and a grating drive mechanism 22 or 42. The set wavelengths of the excitation-side and emission-side light-dispersing devices 2 and 4 can be adjusted at desired wavelengths by directing the inclinations of the diffraction gratings 21 and 41 at predetermined angles by means of the grating drive mechanisms 22 and 42. Since the wavelength λEm of the fluorescence is normally different from the wavelength λEx of the excitation light, different wavelengths are respectively set for the excitation-side and emission-side light-dispersing devices 2 and 4.    Patent Document 1: JP-A 2008-86562